The objective of the proposed project is to further develop and evaluate a noninvasive instrument which will provide information which is pertinent to assessing retinal ischemia in patients with retinal vascular disease. The instrument will measure the electroretinographic response to a flickering light, extract the pertinent information, and present this information, in the form of two numbers, to the clinician. This device will be considerably easier to operate than existing electrodiagnostic systems and will provide relevant, unambiguous information to the clinician. The performance of the device will be evaluated on a population of normal subjects, patients with diabetic retinopathy, and patients with central retinal vein occlusion (CRVO). Measurements from the new device will be compared with information from conventional electroretinographic measurements, fundus photography and fluorescein angiography. In patients with CRVO, the measurements will be correlated with the clinical outcome of the disease. As a secondary goal of the study, novel parameters of the electroretinogram will be extracted to see if changes in waveform shape can be correlated with progression to neovascularization in patients with retinal vascular disease.